Fast pyrolysis is a thermal process during which solid carbonaceous biomass feedstock, i.e., “biomass”, such as wood waste, agricultural waste, etc., is rapidly heated to pyrolysis temperatures of about 400 to about 800° C. (752 to 1,472° F.) in the absence of air using a pyrolysis reactor. Under these conditions, solid, liquid, and gaseous pyrolysis products are formed. A condensable portion (vapors) of the gaseous pyrolysis products is condensed into biomass-derived pyrolysis oil. Conventional biomass-derived pyrolysis oil is generally thermally unstable and acidic (as measured by the total acid number (TAN)), making it corrosive, typically with low energy density relative to hydrocarbon fossil fuels. Thermal instability of biomass-derived pyrolysis oil leads to increased viscosity over time. The low energy density and poor thermal stability of the biomass-derived pyrolysis oil is attributable in large part to oxygenated hydrocarbons in the oil, which undergo secondary reactions during storage. Such oxygenated hydrocarbons include carboxylic acids, phenols, cresols, aldehydes, etc. The oxygenated hydrocarbons in the oil are derived from oxygenated hydrocarbons in the gaseous pyrolysis products produced during pyrolysis of solid biomass.
Biomass-derived pyrolysis oil can be burned directly as fuel for certain boiler and furnace applications, and can also serve as a potential feedstock in the production of biofuels in petroleum refineries or in stand-alone process units. Biomass-derived pyrolysis oil also has the potential to partially replace transportation fuels, thereby reducing the dependency on conventional petroleum and reducing its environmental impact. However, conversion of biomass-derived pyrolysis oil into biofuels suitable for transportation applications in unmodified equipment used for conventional fossil fuels and, in some cases, for production of chemicals, requires full or partial deoxygenation of the biomass-derived pyrolysis oil. While some deoxygenation occurs from the elimination of carbon oxides during conventional pyrolysis of the carbonaceous biomass feedstock, such deoxygenation is insufficient to produce high energy density, thermally stable biomass-derived pyrolysis oils from which biofuels and chemicals are derived.
Most efforts to deoxygenate the biomass-derived pyrolysis oils involve secondary upgrading of the biomass-derived pyrolysis oils after their production, i.e., post-pyrolysis, typically in a separate reactor or downstream process unit. Such secondary upgrading, however, adds unnecessary cost and complexity to the production of low oxygen biomass-derived pyrolysis oil.
Accordingly, it is desirable to provide process for producing biomass-derived pyrolysis oil which requires less or no secondary upgrading. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawing and this background of the invention.